C C C or C C. polyethene (polyethylene)

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1 Polymers Plastics belong to a group of substances called polymers. Polymers are large molecules that are made by linking together many smaller molecules, much like paper clips in a long chain. (In fact, the word polymer comes from two Greek words meaning many parts. ) Different types of small molecules form links in different ways. The types of small units and linkages can be selected to produce materials with desired properties, such as strength, flexibility, transparency, and chemical stability. As consumer needs change, new polymers are designed and manufactured. Plastics are synthetic polymers, but there are many natural polymers as well. ur own cells manufacture complex carbohydrates (polymers of sugars), proteins (polymers of amino acids), and DA (polymers of small units of genetic material). Addition Polymers Addition polymers result from the addition reactions of small subunits that contain double or triple carbon carbon bonds. The small subunits that make up a polymer are called monomers. The monomers in a polymer may all be identical, or two or more monomers may occur in a repeating pattern. Polyethene (commonly called polyethylene) is used for insulating electrical wires and for making plastic containers. Its monomers are ethene (ethylene) molecules that undergo addition reactions with other ethene molecules. As a result, the double bond in each ethene monomer becomes a single bond. The polymerizaton reactions may continue until thousands of ethene molecules have joined the chain plastic a synthetic substance that can be moulded (often under heat and pressure) and retains the shape it is moulded into polymer a molecule that consists of many repeating subunits addition polymer a polymer that is formed when monomer units are linked through addition reactions; all atoms in the monomer are retained in the polymer monomer a molecule that is linked with other similar molecules to form a polymer or ethene ethene ethene polyethene (polyethylene) n Similarly, propene undergoes addition polymerization to produce polypropene, commonly called polypropylene (Figure 1, on the next page). You may have used a polypropylene rope or walked on a polypropylene carpet. The propene molecule can be thought of as an ethene molecule with a methyl, 3, group attached. Therefore, the polymer that is formed contains a long carbon chain with methyl groups attached to every other carbon atom in the chain or 3 3 propene monomers polypropene (polypropylene) 3 3 n EL rganic hemistry 237

Ethene molecules that have other substituted groups produce other polymers. For example, polyvinyl chloride (commonly known as PV) is an addition polymer of chloroethene, 2 5 l.

+ + + l l l l l l vinyl chloride monomers polyvinyl chloride (PV) Figure 1 When the double bonds in propene molecules undergo addition reactions with other propene molecules, the polymer that is

crosslinks covalent bonds that form between polymer chains Figure 2 rosslinks produce a more rigid structure.

2 Ethene molecules that have other substituted groups produce other polymers. For example, polyvinyl chloride (commonly known as PV) is an addition polymer of chloroethene, 2 5 l. PV is used as insulation for electrical wires and drain pipes, and as a coating on raincoat and upholstery fabrics. You may recall performing a test for chlorine in Activity 3.17: lassifying Plastics l l l l l l vinyl chloride monomers polyvinyl chloride (PV) Figure 1 When the double bonds in propene molecules undergo addition reactions with other propene molecules, the polymer that is formed is structurally strong. This polymer, when used in polypropene ropes, has saved climbers lives. crosslinks covalent bonds that form between polymer chains Figure 2 rosslinks produce a more rigid structure. Properties of Addition Polymers Plastics are addition polymers that are chemically unreactive. This property makes them ideal for use as containers for chemicals, solvents, and foods. Plastics are stable because the double bonds of the monomers have been changed to less reactive single bonds. In effect, the unsaturated alkene monomers have been transformed into less reactive saturated alkanes. Plastics are generally flexible and mouldable. The long polymer chains are held together by numerous, but weak, intermolecular forces. These forces allow the polymer chains to slide along each other, making them flexible and stretchable. eating increases the flexibility of plastics because the motion of molecules is increased. The increased motion further disrupts the forces between the molecules. Therefore, plastics can be softened and moulded by heating. Some monomers have two double bonds. These monomers can therefore link to two separate polymer chains at the same time. As well as forming their regular polymer chain, they form strong covalent bonds, called crosslinks, between adjacent polymer chains. The crosslinks hold the adjacent polymer chains firmly together. The more crosslinks there are, the more rigid the plastic is (Figure 2). TRY TIS activity Skewering Balloons The polymers in synthetic rubber are strong, stretchy, and flexible. Just how much can you push them around? Try this! Materials: balloon, thin knitting needle or long bamboo skewer 1. Inflate a large round balloon. Release a little of the air until the balloon is not taut, and tie a knot at the neck. 2. Place the tip of the needle or skewer at the thick part of the balloon, directly opposite the knot. Slowly rotate the needle or skewer and push it into the balloon. ontinue pushing the needle through the balloon and out through the thick area around the knot. (a) Explain your observations. Figure 3 might help! Figure Unit 3 EL

Section 3.18 ondensation Polymers Recall that carboxylic acids react with alcohols to form esters (section 3.13), and with amines to form amides (section 3.15).

3 Section 3.18 ondensation Polymers Recall that carboxylic acids react with alcohols to form esters (section 3.13), and with amines to form amides (section 3.15). These reactions are called condensation reactions. When monomers join, end to end, to form ester or amide linkages, polymers called polyesters and polyamides are produced. Because polyesters and polyamides result from condensation reactions, these polymers are called condensation polymers. To form a polyester or a polyamide, the monomer molecule must have two functional groups, one at each end of the molecule. The functional groups that meet end to end must be a carboxyl group ( ) and either a hydroxyl group ( ) or an amine group ( 2 ). For example, nylon is a polyamide formed from two different monomers: one with a carboxyl group at each end, and the other with another amine group at each end. This arrangement allows an amide to form at each junction of monomers, producing long chains of nylon. polyester a polymer that is formed by condensation reactions resulting in ester linkages between monomers polyamide a polymer that is formed by condensation reactions resulting in amide linkages between monomers condensation polymer a polymer that is formed when monomer units are linked through condensation reactions adipic acid 1,6-diaminohexane nylon 6,6 + 2 n n ylon was designed to be a substitute for silk, so its structure is similar to the structure of silk. ylon production was increased during the Second World War, when nylon was used to make parachutes, ropes, cords for aircraft tires, and even shoelaces for army boots. You probably encounter many polyesters in your daily life. ne of the most familiar polyesters is Dacron, which is found in clothing fabrics (Figure 4). ne of the monomers that is used to produce Dacron has a carboxyl group at each end. The other monomer has a hydroxyl group at each end. An ester linkage is formed at each junction of the monomers, and long polyester chains are produced. Figure 4 This clothing label indicates that the article of clothing is composed of polyester fabric. EL rganic hemistry 239

4 LEARIG TIP Vinyl Some unsaturated hydrocarbon groups have special names. For example, the ethene group is sometimes called a vinyl group. Many synthetic products that are commonly called vinyl are addition polymers of vinyl monomers with a variety of substituted groups. vinyl l l monomer of Saran wrap (with vinyl chloride) monomer of acrylic 3 TRY TIS activity Making ylon (TeacherDemonstration) ne of the early synthetic polymers, nylon, can be made in a lab. It is formed at the boundary of two immiscible reactants (reactants that do not mix), so it can be drawn out as a continuous thread. Materials: eye protection; lab apron; protective gloves; 0.25-mol/Ladipyl chloride dissolved in cyclohexane; 0.5-mol/L1,6-diaminohexane dissolved in 0.5-mol/Lsodium hydroxide solution, a (aq) ; 15-cm length of copper wire; two 50-mLbeakers; water 1. Place 10 mlof the 1,6-diaminohexane solution in one beaker. 1,6-diaminohexane is toxic and an irritant to the eyes, skin, and respiratory system. andle with caution, and wash hands thoroughly after this activity. 2. Tilting the beaker at an angle, slowly add 10 mlof the adipyl choride solution so that two distinct immiscible layers are formed. yclohexane is flammable and irritating to the respiratory system. Keep it away from flames, and do not inhale it. Sodium hydroxide is corrosive. Wear eye protection, a lab apron, and protective gloves. Avoid contact with bare skin. 3. Twist one end of the copper wire into a small hook. Use the hook to pull the nylon film that is formed at the boundary of the two liquid layers. ontinue pulling to extract the nylon strand until it breaks. 4. Place the nylon in the other clean beaker. Rinse the nylon gently with water. 5. Examine the properties of the nylon: for example, its strength, flexibility, and solubility in different solvents. 6. Dispose of the remaining reactants and products as directed by your teacher. monomer of instant glue DID YU KW? ylon ylon was designed in 1935 by Wallace arothers, a chemist who worked for DuPont. The name nylon is a contraction of ew York and London, where research on nylon was done. Properties of ondensation Polymers Intermolecular bonds play an important part in the properties of condensation polymers. Polyamide chains, such as nylon, have amine groups that can hydrogen-bond with the groups on other chains. As a result, polyamide chains form exceptionally strong fibres. Similarly, the strong attractive forces between polar groups in polyesters, such as Dacron, hold the separate polymer chains together, giving them considerable strength. A polymer called Kevlar illustrates the effect of intermolecular bonds in condensation polymers. Kevlar has very special properties. It is stronger than steel and heat-resistant, yet it is lightweight enough to wear. Kevlar is used to make products such as aircraft parts, sports equipment, protective clothing for firefighters, and bulletproof vests for police officers. 240 Unit 3 EL

5 Section 3.18 What gives Kevlar these special properties? The polymer chains form a strong network of hydrogen bonds, which hold adjacent chains together in a sheet-like structure. The sheets are stacked together to form extraordinarily strong fibres. When woven together, these fibres are resistant to damage, even the damage caused by a speeding bullet (Figure 5). DID YU KW? Pulling Threads To make a polymer into a fibre, the polymer must first be heated and melted. The molten polymer is then placed in a pressurized container. It is forced through a small hole, producing a long strand, which is then stretched. This process, called extrusion, causes the polymer chains to orient themselves lengthwise along the direction of the stretch. Intermolecular bonds are formed between the chains, giving the fibres added strength. hopper pellets of polymer hole molten polymer bobbin Figure 5 Kevlar is a synthetic fibre that is silky, soft, and light, yet stronger than steel an extraordinary combination of properties. hemical engineers have used their imagination and expertise to combine these properties to make products where lightweight strength is essential. Kevlar is used in bulletproof vests, protective gloves, tires, racing shoes, fibre optics, and aircraft. DID YU KW? Disappearing Laundry Bags In hospitals, contaminated sheets and towels are sterilized in special laundry facilities. andling these linens, however, is hazardous. rganic chemistry comes to the rescue, with a laundry bag that is made of water-soluble polymers. The dirty laundry is put in the washing machine, still in the bag. The numerous hydroxyl groups allow the bag to dissolve and disappear into the wash water. EL rganic hemistry 241

6 Section 3.18 Questions Understanding oncepts 1. What functional groups, if any, must be present in a monomer that undergoes an addition polymerization reaction? 2. (a) Describe the intermolecular forces of attraction among long addition polymer chains. (b) Why are these polymers more useful, as materials, than their monomers? (c) Why are these polymers more chemically stable than their monomers? 3. Describe a structural feature that is necessary in a monomer added for crosslinking between polymer chains. Include a structural formula to illustrate your answer. 4. What functional group(s) must be present in a monomer of a condensation polymer? 5. Describe the type of chemical bonding within a polyamide chain and the type of chemical bonding between adjacent polyamide chains. 6. (a) What are the typical properties of a plastic? (b) What types of bonding would you expect to find within and between the long polymer molecules? (c) Explain the properties of plastics by referring to their bonding. 7. State the difference in the structures of a polyester and a polyamide. Give an example of each. 8. Describe the role of each type of chemical bond in a polyamide: (a) covalent bonds (b) amide bonds (c) hydrogen bonds Making onnections 9. (a) Research the molecular structures of the reactants that are used to make nylon in the activity on page 240. Use these molecular structures to write the reaction equation for the formation of nylon. ircle the reacting functional groups. (b) The name nylon is often followed by two numbers, as in nylon 6,6. Find out what these numbers represent. G Applying Inquiry Skills 10. Suppose that two new polymers have been designed and synthesized for use as potting materials for plants. (a) List and discuss the properties of two ideal polymers that could be used to hold and supply water for a plant over an extended period of time. (b) Design an experiment to test and compare the two polymers for the properties you listed. Write a brief description of the procedure you would follow, as well as possible interpretations of experimental results. 11. (a) ontact your community recycling facility to find out what types of plastic products are accepted for recycling in your area. If there are some plastics that are not accepted, find out the reasons. (b) Research the molecular structures and functional groups of at least five of these plastics. (c) Summarize your findings, including structural formulas, in a well-organized table. G 12. When household waste is deposited in a landfill site, some of it decomposes. The products of this decomposition may seep into the ground and contaminate water supplies. Work with a partner to complete the following tasks: (a) Brainstorm and list properties that would be ideal for a plastic liner for a landfill site, to contain the potentially toxic seepage. (b) Describe the general structural features of a polymer that would provide the properties you listed. 13. atural rubber is made from a resin that is produced by the rubber tree, evea brasiliensis. Research the commercial production and use of natural rubber, and the circumstances that stimulated the development of synthetic rubber. Write a brief report on your findings. G The superabsorbency of water by sodium polymethylacrylate is ideally suited to its use in baby diapers and other hygiene products. Suggest other applications for which this polymer would be useful. 242 Unit 3 EL

Plastics are synthetic substances that can be moulded (often under heat and pressure) and retain the shape they are moulded into.

5.7: Polymers Plastics are synthetic substances that can be moulded (often under heat and pressure) and retain the shape they are moulded into. Polymers are large molecules that are made by linking together